1. Field of the Invention
The present invention relates in general to an on-demand ad hoc mobile node, a mobile network system and a method thereof. More specifically, the present invention relates to a mobile node, a mobile network system and a method thereof, capable of optimizing a communication path between a source node and a destination node by the movement of a mobile node.
2. Description of the Related Art
A high speed mobile network for constructing a network environment using radio waves or lights instead of cables has become part of every day life. Because no cable wiring is required, the mobile network can be very easily installed, yet provides a very high speed data communication at a speed of 11 Mbps to up to 54 Mbps over broadband radio waves (on the 2.4 GHz or 5 GHz frequency). Typical examples of mobile network construction technologies are ad-hoc technologies and network infrastructure technologies. Ad-Hoc is a connection method for wireless LANs that requires no base station, so that data transmission between mobile computers such as notebook computers can be done with the wireless LAN only. The alternative of ad-hoc is infrastructure, with an Access Point (AP) that functions as a bridge between existing cable networks.
Mobile nodes in an ad-hoc network perform direct communication operations with each other, so connections are still possible in places where no stable framework such as cable LANs or wireless access points are available.
Ad-hoc network routing protocols usually use ad hoc on-demand distance vector (AODV) routing algorithm and proactive algorithm.
According to the proactive algorithm, routing information is periodically broadcasted, so that every node can have the network information. On the other hand, the AODV routing algorithm is a reactive routing protocol, meaning that it establishes a route to a destination node only on demand of a source node. Because the proactive routing protocols periodically transmit a control message for building and maintaining routing tables independently of the data transmission time, they often cause major overhead for network traffic. In contrast, the AODV routing protocol establishes a routing path only on demand, so it creates no extra network overhead. When a link fails, a routing path can be easily recovered and reestablished. Because of these advantages, AODV routing is preferred.
FIG. 1 is a diagram illustrating a configuration of an ad-hoc mobile network system based on AODV routing algorithm. As shown in FIG. 1, a communication path (or routing path) between a source node 1 and a destination node 6 is established, and nodes 2 to 5 exist on the path. To establish a communication path between the node 1 and the node 6, the node 1 broadcasts a route request message (RREQ) to its peripheral nodes. If one of intermediate nodes (i.e., one of nodes 2 to 5) having route information to a destination node or the destination node (i.e., node 6) receives the route request message, a route reply message (RREP) is unicasted into a route where the route request message is transferred. When the node 1 receives the route reply message, a communication path between the node 1 and the node 6 is established.
As shown in FIG. 1, it is also possible that a new node (i.e., node 7) enters the communication range of the node 1. If a new communication path via the node 7 is established between the node 1 and the node 6, the number of intermediate nodes (or hops) is much less than that of the old communication path via the node 2 to the node 6. This feature increases transmission (communication) speed and reduces a possibility of link failure due to the separation of an intermediate node or an exhausted battery.
However, the disadvantage of the related art AODV routing is that the communication path cannot be changed until an originally established communication path is failed. This means that a new node, if there is, is not used very effectively.
In addition, if the number of intermediate nodes is very large, there is a high possibility that one of the intermediate nodes can be separated or battery is soon exhausted, which only causes the link failure. When this occurs, the source node must go through a route searching procedure in order to recover a path. This creates extra traffic for communication (i.e., overhead). Besides, since packet transmission is not possible during the path reestablishment process, it resultantly causes significant inconvenience for users.